Electronic controls and computers are well known in the art of automotive manufacturing. It is not unusual for a late model automobile to have a computer for monitoring and controlling many of its operating systems. Typically an input stage may include data collection by sensors. The collected data is input to a processing stage where an electronic control module interprets the data and calculates appropriate output for delivery to an output stage. Actuators within the output stage convert the appropriate output to a desired physical movement. One such operating system includes the electronic throttle control (ETC). In the ETC system, often referred to as a “drive-by-wire” system, the accelerator pedal is not connected to the throttle body by a cable, as in earlier model vehicles, but rather by an electrical connection between the pedal and a throttle controller, as described by way of example in U.S. Pat. Nos. 5,524,589 and 6,073,610. As described by way of example with reference to U.S. Pat. No. 6,098,971, a potentiometer typically replaces the cable that normally runs to the throttle body and electrical wires send pedal position information to a computer. As a result, the pedal must now have its own springs. However, it is desirable to simulate the mechanical feel of a conventional pedal. With each spring having its own feel and no hysteresis effect as does a cable in a sheath, a spring and mechanical hysteresis device is desirable for operation with the pedal for simulating the mechanical feel. A hysteresis force is a controlled frictional force which simulates the friction created in a conventional pedal as the linkage cable is pushed and pulled through a cable sheath. The hysteresis forces have the beneficial effect to a driver, by way of example, of preventing fatigue, as the force needed to maintain a fixed position of the pedal is less than the force to move the pedal to the fixed position. In addition, the hysteresis force helps enable the vehicle operator to maintain a fixed pedal position over bumpy roads. A pedal position sensor provides an electrical voltage output responsive to pedal angular position. The pedal position sensor typically includes a resistive potentiometer that replaces the cable that normally runs to the throttle body of the vehicle engine. As described in U.S. Pat. No. 6,098,971 to Stege et al., and as is well known in the industry, problems inherent with drive-by-wire systems include the need for the pedal to have its own spring, and with its own spring, the feel of the pedal can change from pedal to pedal and manufacturer to manufacturer. To provide a desirable feel, pedals used with electronic controls have included hysteresis devices that provide varying friction during depressing and releasing of the pedal. Typically, and as further described in U.S. Pat. No. 6,098,971, a pedal module for use with ETC systems includes return springs operable with hysteresis elements that provide a varying force against the pedal when being operated between an idle position and an accelerating control position, by way of example.
Various measures of hysteresis force are defined in vehicle manufacturer's specifications for ETC accelerator pedals. In some cases a constant hysteresis force is specified, but in others a hysteresis force which increases with applied pedal force is preferred. Also, the amount of hysteresis force as a percentage of applied force has generally increased as the specifications have become more refined. The need to provide a mechanism which produces a controllable, and “tuneable,” hysteresis force of significant magnitude presents a challenge to the pedal designer.
With no hysteresis force, the force from the return spring balances the applied pedal force. The hysteresis force is a form of friction force that subtracts from the applied force as the pedal is being depressed and subtracts from the spring force as the pedal is being returned toward its idle position. Such friction force depends on a normal force being generated at a frictional surface. A number of arrangements of springs and friction pads, or washers are known. However, there remains a need for a low cost pedal that is simple to fabricate using plastic molding technology and can be tuned to a broad range of customer requirements.